This invention relates to an improved thermoplastic reinforcing material, which is particularly suitable for the reinforcing and stiffening of materials for use in the manufacture of shoes, and to a method of manufacture of the material.
Thermoplastic reinforcing materials are known and have been used for a long time in the footwear industry, and it is a disadvantage of these known materials that they must first be coated with an adhesive, such as a hot melt adhesive, before they can be bonded to the upper or lining material to be reinforced.
In European patent application no. 183,912 U.S. Pat. No. 4,717,496, a reinforcing material is described which consists of 30 to 80% by weight of filler and 70 to 20% by weight of binder, the particles of filler being formed entirely or at least on their surface of plastic and having a grain size distribution of 50 to 500 micron, and the binder being thermoplastic with adhesive properties in the temperature range 50.degree. to 80.degree. C. As used in connection with the filler, the term plastic is said to refer to those plastics which on the basis of their melt properties alone, are scarcely amenable, if at all, to processing into forms with a large surface area using powder technology methods. Particularly suitable plastics are said to include hard PVC particles and copolymers of vinyl chloride and an alpha-olefine or of styrene and butadiene or propenenitrile, butadiene and styrene. Suitable binders are said to include polycaprolactones, elastomeric polyurethenes, modified polyalkenes and ionomers.
The materials proposed in the European Patent Application demonstrate a number of disadvantages. In order to achieve the stiffness required for use in the footwear industry, it is necessary to use a relatively high weight loading of plastics or plastics coated filler, which increases the cost of the material. The plastics or plastics coated filler is relatively expensive, as it has to be ground to the grain size distribution specified, and it may be difficult to obtain.
It is an object of the present invention to provide a reinforcing material, which is particularly suitable for use in the footwear industry, in which the above disadvantages are reduced or substantially obviated.